b.txt

       user     system      total        real
   0.130000   0.000000   0.130000 (  0.136423)
   0.160000   0.000000   0.160000 (  0.165723)
   0.220000   0.000000   0.220000 (  0.233087)

test.rb

require 'benchmark'

i = 1_000_000

d = {}

Benchmark.bm do |r|
  r.report do
    i.times do
      _ = d[:a] || "lol"
    end
  end

  r.report do
    i.times do
      _ = d.fetch(:a,"lol")
    end
  end

  r.report do
    i.times do
      _ = d.fetch(:a) { "lol" }
    end
  end
end